The manege deposits of the Ioi Mine are deposited along a contact plane betweenq uartzite and sandy slate in the Chichibu Palaeozoic formation which is composed of alternations of quartzite and slate., The deposite consist of the two groups of complicated bedded-veins., The western ore body of Prof., T., Yoshimuras Ioi Type deposit, includes large quantity of manganese dioxide ore., The eastern ore body has the noticeable shape as presented in Fig., 1, being composed mainly of hausmannite, manganese carbonates and manganese silicates., Hausmannite was confirmed by chemical analysis (Table 1) and X ray powder photographs (Tabie 2, No., 1)., The hausmannite occured allo abundantly in the brown earthy spots as shown in the X ray powder photographs (Table 2, No., 2), in the manganese carbonate ore of light pinkcolor., In this deposits there are found such another numerous minerals as follows; pyrrhotite, ala-bandite, arsenopyrite, marcasite (?), pyrite, manganosite, quartz, chalcedony, opal, manganbrucite, pyrochroite (?), manganite (?), galaxite, rhodochrosite, mangancalcite, barite, apatite, adularia, spessartine, tephroite, alleghanyite, manganhedenbergite, rhodonite, dannemorite, mangan tremolite-actinolite, manganphlogopite, chlorite, and penwithite.,